A silencer of this type is known from DE 195 04 223 A1.
Silencers are used in the intake system of engines, e.g. in motor vehicles, for reducing sound emissions. German-Offenlegungsschrift 34 31 078 suggests for this purpose a silencer consisting essentially of an intake pipe which is produced from a sound-absorbing porous material in a certain section thereof, the intake pipe being surrounded by a perforated metal tube in said section. The above-described silencer does not satisfy the demands on the degree of silencing, which are higher than they used to be. Particularly problematic is the silencing of the noise of engines provided with exhaust-driven turbocharger systems. When such turbocharger systems are in operation, pulsation noise is caused, said pulsation noise being generated by minute geometric irregularities of a compressor impeller of the turbocharger. This pulsation noise occurs proportionally to the rotational frequency of the exhaust-driven turbocharger. The frequency band excited is here very large in view of the large range of operating speed. It follows that sound damping over a particularly broad band is here necessary so as to achieve a general reduction of sound emission.
In DE 195 04 223 A1it is suggested that the perforated tube should be used as an intake pipe which is surrounded by a cylinder having a closed, plane surface. Between the inner, perforated intake pipe and the cylinder which concentrically surrounds said intake pipe, a broad continuous annular gap is formed. The openings provided in the perforated intake pipe are arranged in the area of said annular gap, so that said annular gap can communicate with the interior of the intake pipe. The improved silencing characteristics of this silencer are based on air mass exchange and pressure compensation with the annular gap, which can take place through the openings in the intake pipe; the cylinder, which forms the annular gap, prevents pressure losses and causes a further reduction of noise emission. However, not even the silencing degree of this silencer suffices to achieve a broad-band reduction of noise emission especially in the case of supercharged engines.
DE 196 38 304 A1 discloses a silencer which is specially designed for engines provided with turbochargers. This silencer comprises a chamber which is arranged in the flow passage and which is provided with a plurality of annular orifice plates that are arranged in parallel, spaced relationship with one another. Between two neighbouring annular orifice plates, a respective resonance chamber is formed, which leads to sound reduction in a specific frequency range. This silencer has the disadvantage that the orifice plates have edges which are located in the flow path of the gas. The flow resistance caused by these edges impairs the efficiency of the turbocharger system. In addition, the insertion of the orifice plates in the silencer chamber is complicated from the point of view of production technology and entails therefore high costs.
Furthermore, silencer systems are available and are also used in engines, in the case of which a plurality of different silencing elements are arranged in series, said silencing elements being configured for different frequency bands. Silencing systems of this type require, however, an excessive amount of installation space.
In the applicant's post-published prior application DE 103 41 319.7 a silencer is described, which comprises an inner component and an outer component arranged on the outer side of said inner component, said inner component being perforated and said outer component being implemented as a bellows. This kind of silencer has excellent, in particular broadband silencing characteristics.